1. Field of the Invention
This invention relates to a starter motor, and more particularly to a structure for fixing a through bolt of a starter motor.
2. Description of the Prior Art
A conventional starter motor will be first described with reference to FIGS. 4 and 5. The starter motor shown includes an armature rotary shaft 1, an armature core 2 secured by press fitting to an outer periphery of the armature rotary shaft 1, and a commutator 3 fitted at a portion of the armature rotary shaft 1 rearwardly (leftwardly in FIG. 4) of the armature core 2. A yoke 4 which serves as a machine frame and forms a magnetic circuit of the motor is disposed around the armature core 2, and a field coil 5 is disposed on an inner periphery of the yoke 4. A front bracket 6 is fitted at a front end of the yoke 4 while a rear bracket 7 is fitted at a rear end of the yoke 4, and the yoke 4 and front and rear brackets 6 and 7 are secured in an integral relationship to each other by means of a pair of headed through bolts 8 which extend along outer peripheries of the rear bracket 7 and yoke 4 into the front bracket 6. The rear bracket 7 is formed by stamping an iron plate, and a central portion of a rear end wall of the rear bracket 7 is opened as at 7b and extends forwardly to form a forward extension 7a. A bearing 9 is secured by press fitting in an inner periphery of the forward extension 7a of the rear bracket 7 and supports a rear end portion of the armature rotary shaft 1 for rotation thereon. A retaining member 10 having a diameter greater than the rear end opening 7b of the rear bracket 7 is mounted at the rear end of the armature rotary shaft 1 for engaging with the rear bracket 7 to prevent the armature rotary shaft 1 from coming off axially forwardly. A cover 11 is secured to the rear bracket 7 by means of a pair of screws 12 and covers over the retaining member 10 and the rear end of the armature rotary shaft 1. A pair of brush holders 14 are secured to the rear bracket 7 also by means of the screws 12. The brush holders 14 are disposed on the inner side of the rear bracket 7 and individually hold brushes 13 thereon such that they may slidably contact with the commutator 3. A pair of supports 15 for engaging with the heads of the through bolts 8 are secured in an integral relationship to an outer periphery of the rear end of the rear bracket 7 by welding.
An overrunning clutch 16 is provided forwardly of the armature rotary shaft 1, and a pinion shaft 17 is mounted for movement on the armature rotary shaft 1 and connected to be driven by way of the overrunning clutch 16. The pinion shaft 17 has a pinion 17a formed at a forward end thereof. A lever 18 is supported for pivotal motion on the yoke 4 and is held in engagement at an end thereof with a plunger 19a of an electromagnetic switch 19 and at the other end thereof with a rear portion of the overrunning clutch 16.
In operation, when the electromagnetic switch 19 is energized, the plunger 19a is pulled into the electromagnetic switch 19, whereupon the lever 18 is pivoted by the plunger 19a to move the overrunning clutch 16 forwardly. Consequently, the pinion driving shaft 17 is moved forwardly until the pinion 17a thereon is put into meshing engagement with a ring gear of an internal combustion engine, not shown. Meanwhile, upon energization of the electromagnetic switch 19, the motor is energized to produce a turning force, and rotation of the armature rotary shaft 1 of the motor is transmitted to the pinion driving shaft 17 by way of the overrunning clutch 16 to rotate the pinion 17a to cause the engine to start its operation. After starting of the engine, the electromagnetic switch 19 is deenergized, and then the pinion 17a is moved back to its initial position by a return spring (not shown) provided at a suitable location in the motor.
In the conventional starter motor having such a construction as described above, the supports 15 for engaging with the heads of the through bolt 8 are welded in an integral relationship to the rear bracket 7. Accordingly, in case it is necessary to change the positions of the through bolts 8 in accordance with a mounting layout of the starter motor, also the positions of the supports 15 must be changed. Thus, the conventional starter motor has a drawback that, when the mounting layout is different, the rear bracket 7 cannot be commonly used.
Meanwhile, since seats for the heads of the through bolts 8 are each formed from a rear end face of a support 15 and a rear face of the rear bracket 7, it is important to assure a planar alignment of those faces. However, since the separate members are welded to form those faces thereon, it is difficult to secure the supports 15 and the rear bracket 7 in an appropriate positional relationship. Beside, since the outer peripheral edge of the rear end of the rear bracket 7 has a curved or circular shape, it is necessary to arrange the through bolts 8 such that their heads cannot engage with the curved portion of the rear bracket 7. In this manner, the conventional starter motor has another drawback in that it is difficult to assure a planar alignment of the faces of the rear bracket 7 and supports 15.